Police are seen at Aitken Creek Primary School in Craigieburn after students were evacuated. Photo: Wayne Taylor

"All affected schools are expected to be open tomorrow," he said.

Mr Merlino said the incidents had caused stress for school communities.

"These anonymous cowards will feel the full force of the law," Mr Merlino said

Police Chief Commissioner Grahram Ashton said the calls were consistent with those made last week.

He said the calls were automated but just one had an American accent.

The calls either threatened bombings and shootings but in one case there was both.

Chief Commissioner Ashton said the threats were a "hoax scenario" but each one needed to be taken seriously.

"It may be that a particular call that might come in that is not a hoax," he told reporters.

Police have been investigating the calls since Friday.

The calls are not regarded currently as being terrorist-related.

Federal police are investigating the "international elements" of the calls.

The Education Department has also confirmed a number of schools have received threatening calls.

"The safety and wellbeing of our students and staff is always our number one priority, and the Department is taking these incidents, and those occurring last week, very seriously," the statement reads.

"All schools have emergency management plans, and the affected schools have enacted their plans today."

Kooweerup Primary School and Wonthaggi Primary School were both targeted, with Wonthaggi posting to the school's Facebook page that they had been briefly evacuated before being given the all-clear to return to work.